The present invention relates to the field of PIN diodes which are designed to allow a current associated with a first polarity to flow, and to block currents associated with reverse polarity.
FIG. 1 very schematically shows the general shape of a PIN diode. The diode comprises a low doped substrate 1, the doping level being usually referenced N.sup.- or I to indicate that the doping is close to the intrinsic level, for example 5.10.sup.14 atoms/cm.sup.3. The rear surface of substrate 1 comprises an N.sup.+ layer with a highly doped level, for example 10.sup.21 atoms/cm.sup.3. This surface is coated with a cathode metallization 3. In the front surface is formed a P-type region 4 on which is formed an anode metallization 5.
Normally, the voltage drop across the terminals of such a diode, when conductive, is about 0.6-0.7 volt. However, if a voltage is abruptly applied in the forward direction across the diode, an initial overvoltage peak (peak on), associated with the charges in the intrinsic area, appears.
FIG. 2 shows the voltage variation as a function of time when a direct voltage is abruptly applied across the diode. It can be noted that, during a period of about 200 ns, an initial overvoltage V.sub.p of about 10-50 volts can occur before decreasing again to the normal forward voltage V.sub.F of the diode.
This switching-on delay of the diode can be particularly impairing, for example when such a diode is associated in parallel with a protection component such as an avalanche thyristor.
Thus, an object of the invention is to provide a PIN diode structure avoiding the above peak on phenomenon.